(1) Field of the Invention
The invention relates to a circuit arrangement for igniting four thin silicon rods in a reactor for producing from the thin silicon rods silicon rods according to the Siemens process and for starting up such reactor. Also described is a method for igniting the thin silicon rods and for starting up, i.e., commencing operation of the reactor.
(2) Description of Related Art
The document DE 20 2004 014 812 U1 describes a device for supplying a reactor for producing silicon rods according to the Siemens process, which has first supply means for supplying a voltage and second supply means for supplying a voltage. The first supply means is provided to supply a voltage to the thin silicon rods during a startup phase of the deposition process, i.e., during ignition of the thin silicon rods and startup of the reactor. The second voltage supply means is provided to ensure that a voltage is supplied to the thin silicon rods and the developing silicon rods subsequent to the startup phase during operation.
During the startup phase, the thin silicon rods are supplied by the first supply means with a so-called medium voltage which is greater than 2500 V. Such high voltages are capable of igniting the thin silicon rods. After all silicon rods have been ignited, the startup phase ends. The voltage supply of the thin silicon rods and of the silicon rods formed thereon is then assumed by the second supply means, which supplies the thin silicon rods with a voltage of less than 2500 V.
In the operating the phase, the thin silicon rods and the silicon rods, respectively, are connected in series and the series connection is supplied with a voltage from the second supply means. Alternatively, the thin silicon rods and/or the silicon rods can, during the operating phase, be initially individually supplied with the voltage provided by the second supply means, or supplied with the voltage in groups, or connected in series. The configuration between the various switching arrangements can be changed during the operating phase, depending on the electrical resistance of the silicon rods and the power to be dissipated in the silicon rods.
In the disclosed configuration, the device described in the aforementioned document has not met with acceptance in practical applications. Instead, devices have been constructed in practice where power switches are arranged in series with the input terminals of the second voltage supply means. However, the power switches are technically complex and expensive, in particular because they need to be suitable for medium voltages. In addition, they must be capable of carrying currents in excess of 1000 A during the operating phase. Because this is a mechanical component, the power switch requires maintenance during the service life of the reactor.